Studies of the representation of selected speech sounds in the discharge patterns of auditory nerve fibers are proposed. The broad, long-term goal is to provide the basis for a functional understanding of the neural processing of speech, by describing the neural representation of selected speech sounds in the auditory nerve. The peripheral processing of speech is important for normal speech perception, since hearing loss of cochlear origin can interfere with speech communication, even when amplification is provided. Previous investigations have concentrated on the encoding of spectral information in simple vowels and consonant- vowel syllables. The proposed experiments extend that work to the stop consonants /d/ and /t/ in final and medial positions, which occur frequently in connected speech. Natural speech will be used, to ensure that the dynamic cues that typify real speech are present. The studies will examine the encoding of the temporal and spectral cues that underlie the voiced-voiceless phonemic distinction. The responses of single fibers of the chinchilla auditory nerve will be measured; chinchillas can resolve /d/ from /t/ in psychophysical experiments. Specific Aim 1 is to describe the neural representation of stop consonants /d/ and /t/ in word- final position. The response patterns will be compared to responses to the same consonants in word-initial position, there they are cued by different temporal and spectral patterns. Specific Aim 2 is to determine the influence of acoustic information in a preceding vowel segment on the neural response to the consonant segment. The experiment will examine the representation of syllables that are digitally edited to remove information that is important for the identity of the consonant. Specific Aim 3 is to describe the representation of stop consonants /t/ and /d/ in medial position, between two vowels. The acoustic cues for medial /d/ and /t/ differ from the cues for /d/ and /t/ in initial or final position. The extent to which this acoustic variability is preserved in neural responses will be determined.